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use crate::{
stream::{OperatorBuilder, OperatorContext, StreamBuilder},
types::{Data, DataMessage, MaybeKey, Message, Timestamp},
};
/// Inspect messages in a stream without modifying them
pub trait Inspect<K, V, T>: super::sealed::Sealed {
/// Observe values in a stream without modifying them.
/// This is often done for debugging purposes or to record metrics.
///
/// Inspect takes a closure of function which is called on every data
/// message.
///
/// To inspect the current event time see [`crate::operators::timely::InspectFrontier::inspect_frontier`].
///
/// ```rust
/// use malstrom::operators::*;
/// use malstrom::runtime::SingleThreadRuntime;
/// use malstrom::snapshot::NoPersistence;
/// use malstrom::sources::{SingleIteratorSource, StatelessSource};
/// use malstrom::worker::StreamProvider;
/// use malstrom::sinks::{VecSink, StatelessSink};
///
/// let sink = VecSink::new();
/// let sink_insepct = sink.clone();
///
/// let sink_output = VecSink::new();
///
/// SingleThreadRuntime::builder()
/// .persistence(NoPersistence)
/// .build(move |provider: &mut dyn StreamProvider| {
/// provider.new_stream()
/// .source("numbers", StatelessSource::new(SingleIteratorSource::new(0..100)))
/// .
/// inspect("inspect", move |msg, _ctx| sink_insepct.give(msg.clone()))
/// .sink("sink", StatelessSink::new(sink_output));
/// })
/// .execute()
/// .unwrap();
///
/// let expected: Vec<i32> = (0..100).collect();
/// let out: Vec<i32> = sink.into_iter().map(|x| x.value).collect();
/// assert_eq!(out, expected);
/// ```
fn inspect(
self,
name: &str,
inspector: impl FnMut(&DataMessage<K, V, T>, &OperatorContext) + 'static,
) -> StreamBuilder<K, V, T>;
}
impl<K, V, T> Inspect<K, V, T> for StreamBuilder<K, V, T>
where
K: MaybeKey,
V: Data,
T: Timestamp,
{
fn inspect(
self,
name: &str,
mut inspector: impl FnMut(&DataMessage<K, V, T>, &OperatorContext) + 'static,
) -> StreamBuilder<K, V, T> {
let operator =
OperatorBuilder::direct(name, move |input, output, ctx| match input.recv() {
Some(Message::Data(d)) => {
inspector(&d, ctx);
output.send(Message::Data(d));
}
Some(x) => output.send(x),
None => (),
});
self.then(operator)
}
}
#[cfg(test)]
mod tests {
use itertools::Itertools;
use crate::{
operators::*,
sinks::StatelessSink,
sources::{SingleIteratorSource, StatelessSource},
testing::{get_test_rt, VecSink},
};
#[test]
fn test_inspect() {
let inspect_collector = VecSink::new();
let output_collector = VecSink::new();
let input = vec!["hello", "world", "foo", "bar"];
let expected = input.clone();
let rt = get_test_rt(|provider| {
let inspect_collector = inspect_collector.clone();
provider
.new_stream()
.source(
"source",
StatelessSource::new(SingleIteratorSource::new(input.clone())),
)
.inspect("inspect", move |x, _| {
inspect_collector.give(x.value.to_owned())
})
.sink("sink", StatelessSink::new(output_collector.clone()));
});
rt.execute().unwrap();
assert_eq!(inspect_collector.drain_vec(..), expected);
// check we still get unmodified output
assert_eq!(
output_collector.into_iter().map(|x| x.value).collect_vec(),
expected
);
}
}